   "Yields the next state of the board."
   [board]
   (vec (map step-row (window (repeat nil) board))))
+
+;; compare indexed-step the index-free:
+(- (nth (iterate indexed-step glider) 8)
+   (nth (iterate index-free-step glider) 8))
+;;=> true or should be:
+
 
 (defn step 
  "Yields the next state of the world"

           (assoc-in new-board [x y] new-liveness)))
      board (for [x (range h) y (range w)] [x y]))))

(defn window
  "Returns a lazy sequence of 3-item windows centered
   around each item of coll, padded as necessary with

      3 :on
      nil)))

;; the new idexed-step function depending on index free helper functions:
(defn- step-row
  "Yields the next state of the center row."
  [rows-triple]
